There are services that send users emails, such as magazines by email. The amount of data sent by email has increased. For this reason, there have been cases where the amount of data that recipient users receive is reduced. For example, Patent Literature 1 discloses an information transmission method that automatically inserts an identification code in header information of divided emails with an attached image file separately from a user operation in order to transfer the emails to a relay server. The relay server integrates the divided emails, adds a URL storing the attached file to a notification mail, and then sends it. This allows backward compatibility and compatibility between various models.